This invention relates to machines for applying a printed stamp to postal items.
When items are to be carried by a postal authority for delivery to a destination address, payment for carriage of the item is made to the postal authority by purchase of one or more postage stamps which are then affixed to the postal item. The stamps affixed to the postal item provide an indication during subsequent handling of the postal item by the postal authority that a postage charge has been paid and the amount or value of the postage charge paid.
The purchase and affixing of postage stamps is inconvenient particularly for regular senders of postal items requiring different values of postage such as small commercial users of the postal service. In order to overcome the need for purchase of postage stamps prior to despatch of postal items, franking machines were introduced. Franking machines are operated by persons or companies desiring to despatch postal items and are operated under licence from the postal authority. The franking machine is caused to print on the postal item a frank impression of a form prescribed by the postal authority which includes an impression of the value of postage franked on the item. In order for the user of the franking machine to be able to account to the postal authority for the value of postage used to the satisfaction of the postal authority, it has been necessary to provide the franking machine with accounting means to maintain an accurate record of the usage of the machine and the accumulated value of franking applied by the machine. Commonly, the postal authority requires prepayment for usage of the machine. Accordingly the machine includes a register to record the value of credit, purchased by the user from the postal authority, which remains available for usage in franking. The machine is constructed such that, when the registered value of credit decreases to a predetermined low limit, the machine locks and prevents further usage of the machine until additional credit has been entered in the register of the machine by the postal authority in response to payment by the user.
Modern franking machines utilise electronic circuits for carrying out accounting and control functions within the machine. These circuits include a micro-processor and memory devices providing registers for registering accounting values. The registers usually include a descending register into which the value of purchased credit is entered and which is decremented during usage of the machine by the value of franking used in each franking transaction. The registers also include an ascending register to register the accumulated value of franking used and an items register for registering the number of mail items franked by the machine. In order to maintain integrity of the values registered in the various registers, each of the registers is replicated, each replication storing corresponding values. Thus if due to a fault in the operation of the electronic circuits the value registered in one of the replications of a register differs from the value registered in the other replications of that register an indication is provided that a fault has occurred and the true accounting value can be retrieved from the other replications of that register.
If the electronic accounting circuits and the value setting mechanisms by which print elements for printing the value of franking are unprotected, the values registered in the registers and/or the values of postage printed in the franking could be changed by anyone with fraudulent intent. Accordingly it has been necessary to house the circuitry and printing mechanism in a secure manner such as to prevent unauthorised access to these parts of the machine.
The provision of replicated registers and particularly the provision of a secure housing for the circuits and print setting mechanism adds greatly to the cost of manufacturing franking machines. As a result franking machines are too expensive for purchase by users who despatch relatively small quantities of postal items and therefore users who despatch relatively small quantities of postal items are compelled to use postage stamps which may be inconvenient, time consuming and in addition are somewhat un-hygienic to use.